In the prior art and specifically in U.S. Pat. No. 3,921,916 it is suggested that a monocrystalline crystallographically oriented silicon wafer may be selectively etched to form one or more reproducible channels of a specific form in the wafer body. The specific type of the channel described in that patent has a rectangular entrance cross-section which continues to an intermediate rectangular cross-section, smaller than the entrance cross-section, and thento an exit cross-section which has a shape other than rectangular. A channel of this specific type is established by either of two disclosed processes, both of which utilize a heavily doped p+ layer (patterned in the one process and unpatterned in the other) as an etchant barrier. In the two processes, a silicon wafer is heavily doped to place it near or at saturation from one major face to form the p+ etchant barrier. Therefore, patterned anisotropic etching from the opposite major face proceeds until the p+ barrier is reached. The anisotropic etching results in a rectangular entrance cross-section and a rectangular intermediate cross-section defining a membrane smaller in size than the entrance cross-section.
In the application of one process, the etching process is continued from the entrance side until an opening is made through the membrane. The other process utilizes patterned isotropic etching from the opposite side (exit side) of the nozzle to complete a passage through the membrane to the intermediate cross-section.
Although these prior art processes may provide satisfactory ink jet nozzle structures, both of the described processes and the resulting structures have inherent problems. For example, due to inherent wafer thickness variations and isotropic etch nonuniformities, these processes require extensive mechanical and/or chemical polishing of both major surfaces of the wafer to improve dimensional control of the resulting nozzle structures. This is a costly processing step. Additionally, the nozzle structures produced by these processes have heavily saturated p+ regions surrounding the exit openings, and these regions tend to be brittle and thus subject to failure when exposed to high fluid pressures or pressure transients typically present in ink jet printing systems.